Core-sheath composite fiber for artificial hair, headwear product including same, and production method for same

ABSTRACT

A core-sheath conjugate fiber for artificial hair includes a core part and a sheath part. The core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape or an elliptical cross sectional shape, and has a core-to-sheath area ratio of core:sheath=3:7 to 8:2 in a fiber cross section. The sheath part contains a polyamide-based resin composition containing a polyamide-based resin. The core part has a modified flat two-lobed cross sectional shape or a modified elliptical cross sectional shape including a pair of protrusions protruding from the center side toward the outer circumferential side along a minor axis direction of the fiber cross section. A core-sheath conjugate fiber for artificial hair having a touch close to that of human hair, an excellent combing property, and a good curl setting property, a hair ornament product including the same, and a method for producing the same are provided.

TECHNICAL FIELD

One or more embodiments of the present invention relate to a core-sheath conjugate fiber for artificial hair capable of being used as an alternative to human hair, a hair ornament product including the same, and a production method therefor.

BACKGROUND

Conventionally, human hair is used for hair ornament products such as hairpieces, hair wigs, hair extensions, hair bands, and doll hair. However, in recent years, it is becoming difficult to obtain human hair, and thus there is an increasing demand for artificial hair capable of being used as an alternative to human hair.

Such artificial hair is required to have a touch and appearance close to those of human hair, and examples of synthetic fibers that can be used as materials of artificial hair include acrylic-based fibers, vinyl chloride-based fibers, vinylidene chloride-based fibers, polyester-based fibers, polyamide-based fibers, and polyolefin-based fibers. In particular, a core-sheath conjugate fiber containing polyester as a core component and polyamide as a sheath component has been developed as a core-sheath conjugate fiber for artificial hair having a texture close to that of human hair and excellent durability and heat resistance (Patent Document 1).

In Patent Document 1, durability and heat resistance of the core-sheath conjugate fiber for artificial hair are increased by setting a viscosity ratio a/b between a melt viscosity a of polyester and a melt viscosity b of polyamide at 285° C. to 0.5 to 2.5.

Patent Document

-   Patent Document 1: WO 2017/187843

As described above, the fiber described in Patent Document 1 is a core-sheath conjugate fiber that contains polyester as the core component and polyamide as the sheath component. When curls are set using a hair iron or the like, the curl setting property of the core-sheath conjugate fiber for artificial hair is not sufficiently high because a curl setting property obtained with the use of polyamide, which is used as the sheath component, is bad compared with that obtained with the use of polyester, and therefore, a further improvement is desired.

SUMMARY

One or more embodiments of the present invention provide a core-sheath conjugate fiber for artificial hair that has a touch close to that of human hair and an excellent combing property, and also has a good curl setting property, a hair ornament product including the same, and a method for producing the same.

One or more embodiments of the present invention relate to a core-sheath conjugate fiber for artificial hair including a core part and a sheath part, wherein the core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape or an elliptical cross sectional shape, and has a core-to-sheath area ratio of core:sheath=3:7 to 8:2 in a fiber cross section, the sheath part is comprised of a polyamide-based resin composition that contains a polyamide-based resin, and the core part has a modified flat two-lobed cross sectional shape or a modified elliptical cross sectional shape including a pair of protrusions protruding from the center side toward the outer circumferential side along a minor axis direction of the fiber cross section.

Furthermore, one or more embodiments of the present invention relate to a hair ornament product including the core-sheath conjugate fiber for artificial hair.

Furthermore, one or more embodiments of the present invention relate to a method for producing the core-sheath conjugate fiber for artificial hair, including a step of melt spinning a core part resin composition and a sheath part resin composition using a core-sheath conjugate nozzle.

The core-sheath conjugate fiber for artificial hair of one or more embodiments the present invention has not only a touch close to that of human hair and an excellent combing property, but also a sufficiently high curl setting property, and is suitable as a material of hair ornament products.

According to the production method of one or more embodiments of the present invention, it is possible to obtain a core-sheath conjugate fiber for artificial hair that has not only a touch close to that of human hair and an excellent combing property, but also a sufficiently high curl setting property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a fiber cross section of a core-sheath conjugate fiber for artificial hair according to one or more embodiments of the present invention.

FIG. 2 is a laser microscopic photograph of a fiber cross section of a fiber of Example 1.

FIG. 3 is a laser microscopic photograph of a fiber cross section of a fiber of Comparative Example 1.

FIG. 4 is a laser microscopic photograph of a fiber cross section of a fiber of Comparative Example 3.

DETAILED DESCRIPTION

One or more embodiments of the present invention were devised to address the above-described problem of conventional technology, i.e., providing a core-sheath conjugate fiber for artificial hair (hereinafter also simply referred to as a “core-sheath conjugate fiber”) that has an excellent curl setting property. It was found that, conventionally, it had been difficult to obtain a core-sheath conjugate fiber for artificial hair that has a sufficiently high curl setting property when the fiber has a core-sheath structure including a core part and a sheath part (fiber) that have similar shapes, but if a fiber and its core part have specific cross sectional shapes, a sufficiently high curl setting property can be imparted to the fiber.

Shape of Core-Sheath Conjugate Fiber

In one or more embodiments of the present invention, a core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape or an elliptical cross sectional shape, and may have a flat two-lobed cross sectional shape. Also, a core part has a modified flat two-lobed cross sectional shape including a pair of protrusions protruding from the center side toward the outer circumferential side along a minor axis direction of a fiber cross section or a modified elliptical cross sectional shape including a pair of protrusions protruding from the center side toward the outer circumferential side along the minor axis direction of the fiber cross section, and may have a modified flat two-lobed cross sectional shape.

In a flat two-lobed shape, two lobal portions having a shape selected from the group consisting of a circular shape and an elliptical shape are connected via recessed portions. The circular or elliptical shape referred to here does not absolutely have to be a continuous arc, and may also be a substantially circular shape or a substantially elliptical shape that is partially deformed, as long as no acute angle is formed.

The modified flat two-lobed shape is obtained by modifying the flat two-lobed shape so as to include a pair of protrusions protruding from the center side toward the outer circumferential side along the minor axis direction of the fiber cross section. In the flat two-lobed shape, two lobal portions having a shape selected from the group consisting of a circular shape and an elliptical shape are connected via recessed portions, whereas in the modified flat two-lobed shape, the two lobal portions having a shape selected from the group consisting of a circular shape and an elliptical shape are connected via the protrusions.

Regarding the cross sectional shapes, no consideration is given to asperities with a size of 2 μm or less generated at the outer circumference of the fiber and the outer circumference of the core part due to an additive or the like that may be contained in the core-sheath conjugate fiber for artificial hair according to one or more embodiments of the present invention.

FIG. 1 is a schematic view showing a fiber cross section of a core-sheath conjugate fiber for artificial hair according to one or more embodiments of the present invention. A core-sheath conjugate fiber 1 for artificial hair according to this embodiment includes a sheath part 10 and a core part 20 and has a flat two-lobed cross sectional shape in which two elliptical portions are connected via recessed portions.

In the fiber cross section of the core-sheath conjugate fiber for artificial hair, a straight line with the largest length among an axisymmetric axis and straight lines connecting any two points on the outer circumference of the fiber cross section so as to be in parallel to the axisymmetric axis corresponds to a major axis of the fiber cross section, and the direction of the straight line and directions parallel to this direction correspond to a major axis direction. Also, a straight line connecting two points so as to have the largest length when connecting any two points on the outer circumference of the fiber cross section so as to be perpendicular to the major axis of the fiber cross section corresponds to a minor axis of the fiber cross section, and the direction of the straight line and directions parallel to this direction correspond to the minor axis direction.

It is preferable that the length (represented by “L”) of the major axis of the fiber cross section and the length (represented by “S”) of the minor axis of the fiber cross section satisfy the equation (1) below.

L/S=1.1 or more and 2.0 or less  (1)

As shown in FIG. 1, the core part 20 has a modified flat two-lobed shape including a pair of protrusions 30 protruding from the center side toward the outer circumferential side along the minor axis direction of the fiber cross section, and two elliptical portions are connected via the protrusions 30. Alternatively, it can also be said that the core part 20 has a modified elliptical shape including the pair of protrusions 30 protruding from the center side toward the outer circumferential side along the minor axis direction of the fiber cross section.

It is preferable that, in the core part cross section, the length (represented by “Lc”) of a major axis of the core part cross section, which is a straight line with the largest length among an axisymmetric axis and straight lines connecting any two points on the outer circumference of the core part cross section so as to be in parallel to the axisymmetric axis, and the length (represented by “Sc”) of a minor axis of the core part cross section, which is a straight line connecting two points so as to have the largest length when connecting any two points on the outer circumference of the core part cross section so as to be perpendicular to the major axis of the core part cross section, satisfy the equation (2) below.

Lc/Sc<L/S  (2)

In one or more embodiments of the present invention, the core-sheath conjugate fiber for artificial hair has a fiber cross section whose external shape is a flat two-lobed shape. Accordingly, the area of flat portions in the surface of the fiber decreases, and thus reflection of light, which is remarkable in flat portions, is reduced, and the fiber is likely to have gloss close to that of human hair. Also, in one or more embodiments of the present invention, the surface of the core-sheath conjugate fiber for artificial hair, i.e., the outer peripheral shape of the fiber cross section may be comprised of smooth asperities. Accordingly, the area of contact between fibers or between fibers and a comb passed therethrough decreases, and thus a touch dose to that of human hair and a good combing property are realized.

A feature of one or more embodiments of the present invention is the core part including the pair of protrusions along the minor axis direction of the fiber in the fiber cross section, and a good curl setting property can be realized owing to this feature. Here, in the case where the cross sectional shape of the fiber cross section, i.e., the outer peripheral shape of the sheath part is the flat two-lobed shape, which is a preferable form, the curl setting property is further enhanced if a connecting line that connects mutually opposite recessed portions of the fiber cross section overlaps a connecting line that connects the pair of protrusions of the core part.

In one or more embodiments of the present invention, the core-sheath conjugate fiber for artificial hair has a fiber cross section having the flat two-lobed shape. Accordingly, a bending moment in the direction of the connecting line connecting the recessed portions and directions parallel to this direction, i.e., a bending moment in the minor axis direction of the fiber is likely to be smaller than a bending moment in the major axis direction of the fiber, which intersects the connecting line preferably at right angles, and therefore, the core-sheath conjugate fiber is likely to be bent in the minor axis direction at the time of bending deformation. In this configuration, the cross sectional shape of the core part includes the pair of protrusions protruding in mutually opposite directions from the center side toward the outer circumferential side along the minor axis direction of the fiber. Accordingly, in the minor axis direction of the fiber, a core-to-sheath line ratio that indicates the ratio between a portion of a line segment occupied by the core part and a portion of the line segment occupied by the sheath part is such that the ratio of the portion occupied by the core part is substantially large. Therefore, even if the content of a polyamide-based resin in the fiber as a whole is high, properties of the core part comprised of a polyester-based resin or the like are prominent in the minor axis direction of the fiber and can compensate for properties of the polyamide-based resin whose curl setting property is low, and thus a fiber that has a very high curl setting property can be obtained.

The core-sheath conjugate fiber for artificial hair has a core-to-sheath area ratio in the range of core:sheath=3:7 to 8:2, and may be in the range of 4:6 to 7:3. If the core-to-sheath area ratio is in this range, the bending moment, which is a physical property relating to the touch, texture, and the like, is close to that of human hair, and thus artificial hair with a quality similar to that of human hair is likely to be obtained.

If the ratio of the core part is low, the bending moment tends to be smaller than that of human hair. On the other hand, if the ratio of the core part is high, the bending rigidity value tends to be large, and the layer of the sheath part in a cross section becomes extremely thin and accordingly, the core is likely to be exposed, which may lead to the sheath part separating from the core part. It is preferable that the core part is completely covered by the sheath part without being exposed to the fiber surface.

The above-described cross sectional shapes of the fiber and the core part and the core-to-sheath area ratio can be controlled by using a nozzle (pores) with a shape dose to the target cross sectional shape.

From the viewpoint of suitability for artificial hair, the core-sheath conjugate fiber for artificial hair has a single fiber fineness of preferably 10 dtex or more and 150 dtex or less, more preferably 30 dtex or more and 120 dtex or less, even more preferably 40 dtex or more and 100 dtex or less, and even more preferably 50 dtex or more and 90 dtex or less.

In a mass of the core-sheath conjugate fibers for artificial hair according to one or more embodiments of the present invention, e.g., a fiber bundle of the core-sheath conjugate fibers for artificial hair, all fibers do not necessarily have to have the same fineness and the same cross sectional shape, and fibers having different values of fineness and different cross sectional shapes may be mixed.

Composition of Core-Sheath Conjugate Fiber

In one or more embodiments of the present invention, the sheath part is comprised of a polyamide-based resin composition that contains a polyamide-based resin, i.e., a polyamide-based resin composition containing a polyamide-based resin as a main component, and accordingly, the core-sheath conjugate fiber has a good touch. In one or more embodiments of the present invention, when the total weight of the polyamide-based resin composition is taken as 100% by weight, the “polyamide-based resin composition containing a polyamide-based resin as a main component” contains the polyamide-based resin in an amount of 67% by weight or more, preferably 75% by weight or more, even more preferably 85% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more.

The polyamide-based resin means a nylon resin obtained through polymerization of one or more selected from the group consisting of lactam, aminocarboxylic acid, a mixture of dicarboxylic acid and diamine, a mixture of a dicarboxylic acid derivative and diamine, and a salt of dicarboxylic acid and diamine.

Specific examples of the lactam include, but are not particularly limited to, for example, 2-azetidinone, 2-pyrrolidinone, δ-valerolactam, ε-caprolactam, enantholactam, capryllactam, undecalactam, and laurolactam. Of these lactams, it is preferable to use ε-caprolactam, undecalactam, and laurolactam, and more preferable to use ε-caprolactam. These lactams may be used alone or in a combination of two or more.

Specific examples of the aminocarboxylic acid include, but are not particularly limited to, for example, 6-aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid. Of these aminocarboxylic acids, it is preferable to use 6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid, and more preferable to use 6-aminocaproic acid. These aminocarboxylic acids may be used alone or in a combination of two or more.

Specific examples of the dicarboxylic acid that can be used for the mixture of dicarboxylic acid and diamine, the mixture of a dicarboxylic acid derivative and diamine, or the salt of dicarboxylic acid and diamine include, but are not particularly limited to, for example: aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brasylic acid, tetradecanedioic acid, pentadecanedioic acid, and octadecanedioic acid; alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Of these dicarboxylic acids, it is preferable to use adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, and isophthalic acid, and more preferable to use adipic acid, terephthalic acid, and isophthalic acid. These dicarboxylic acids may be used alone or in a combination of two or more.

Specific examples of the diamine that can be used for the mixture of dicarboxylic acid and diamine, the mixture of a dicarboxylic acid derivative and diamine, or the salt of dicarboxylic acid and diamine include, but are not particularly limited to, for example: aliphatic diamines such as 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 2-methyl-1,5-diaminopentane (MDP), 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononan, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane, 1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diamines such as cyclohexanediamine and bis-(4-aminohexyl)methane; and aromatic diamines such as m-xylylenediamine and p-xylylenediamine. Of these diamines, it is preferable to use an aliphatic diamine, and more preferable to use hexamethylenediamine. These diamines may be used alone or in a combination of two or more.

The polyamide-based resin (alternatively referred to as a “nylon resin”) is not particularly limited, but it is preferable to use, for example, Nylon 6, Nylon 66, Nylon 11, Nylon 12, Nylon 6/10, Nylon 6/12, semi-aromatic nylon containing the Nylon 6T and/or 61 unit, copolymers of these nylon resins, or the like. It is more preferable to use Nylon 6, Nylon 66, or a copolymer of Nylon 6 and Nylon 66.

The polyamide-based resin can be produced for example, using a polyamide-based resin polymerization method in which a raw material for the polyamide-based resin is heated in the presence or absence of a catalyst. During the polymerization, stirring may or may not be performed, but it is preferable to perform stirring in order to obtain a uniform product. The polymerization temperature can be set as appropriate according to the degree of polymerization, the reaction yield, and the reaction time of a target polymer, but it is preferable to set the temperature to a low temperature in consideration of the quality of a finally obtained polyamide-based resin. The reaction ratio can also be set as appropriate. The pressure is not limited, but it is preferable to reduce the pressure in the system in order to efficiently let volatile components move to the outside of the system.

The polyamide-based resin used in one or more embodiments of the present invention may have a terminal end that is capped by an end-capping agent such as a carboxylic acid compound or an amine compound as necessary. The concentration of terminal amino groups or terminal carboxyl groups in a nylon resin obtained when a terminal end is capped by adding monocarboxylic acid or monoamine is lower than that when such an end-capping agent is not used. On the other hand, the total concentration of terminal amino groups and terminal carboxyl groups does not change when a terminal end is capped by dicarboxylic acid or diamine, but the concentration ratio between terminal amino groups and terminal carboxyl groups changes.

Specific examples of the carboxylic acid compound include, but are not particularly limited to, for example: aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, myristoleic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and arachic acid; alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid and methylcyclohexanecarboxylic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, ethylbenzoic acid, and phenylacetic acid; aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brasylic acid, tetradecanedioic acid, pentadecanedioic acid, and octadecanedioic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid.

Specific examples of the amine compound include, but are not particularly limited to, for example: aliphatic monoamines such as butylamine, pentylamine, hexylamine, heptylamine, octylamine, 2-ethylhexylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, octadecylamine, nonadecylamine, and icosylamine; alicyclic monoamines such as cyclohexylamine and methylcyclohexylamine; aromatic monoamines such as benzylamine and β-phenylethylamine; aliphatic diamines such as 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononan, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diamino pentadecane, 1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diamines such as cyclohexanediamine and bis-(4-aminohexyl)methane; and aromatic diamines such as xylylenediamine.

The terminal group concentration of the polyamide-based resin is not particularly limited, but the terminal amino group concentration may be high, for example, when it is necessary to increase the dyeability for fiber uses or when designing a material suitable for alloying for resin uses. On the other hand, the terminal amino group concentration may be low, for example, when it is required to suppress coloring or gelation under extended aging conditions. Furthermore, the terminal carboxyl group concentration and the terminal amino group concentration may be both low when it is required to suppress reproduction of lactam during re-melting, yarn breakage during melt spinning due to production of oligomer, mold deposit during continuous injection molding, and generation of die marks during continuous extrusion of a film. It is preferable to adjust the terminal group concentration according to the applications, but the terminal amino group concentration and the terminal carboxyl group concentration are both preferably 1.0×10⁻⁵ to 15.0×10⁻⁵ eq/g, more preferably 2.0×10⁻⁵ to 12.0×10⁻⁵ eq/g, and even more preferably 3.0×10⁻⁵ to 11.0×10⁻⁵ eq/g.

Furthermore, the end-capping agent may be added using a method in which the end-capping agent is added simultaneously with raw materials such as caprolactam at the initial stage of polymerization, a method in which the end-capping agent is added during polymerization, a method in which the end-capping agent is added when a nylon resin in a molten state is caused to pass through a vertical stirring thin-film evaporator, or the like. The end-capping agent may be added without any treatment, or in the form of being dissolved in a small amount of solvent.

From the viewpoint of physical properties of the resin, versatility, and the cost, the polyamide-based resin may be a polyamide-based resin mainly containing at least one selected from the group consisting of Nylon 6 and Nylon 66. In the present disclosure, the “polyamide-based resin mainly containing at least one selected from the group consisting of Nylon 6 and Nylon 66” means a polyamide-based resin that contains Nylon 6 and/or Nylon 66 in an amount of 80 mol % or more.

The polyamide-based resin composition constituting the sheath part may further contain other resins in addition to the polyamide-based resin. Examples of the other resins include a vinyl chloride-based resin, a modacrylic-based resin, a polycarbonate-based resin, a polyolefin-based resin, and a polyphenylenesulfide-based resin. These resins may be used alone or in a combination of two or more.

From the viewpoint of improving the curl setting property, in one or more embodiments of the present invention, the core part may be comprised of a polyester-based resin composition that contains a polyester-based resin, i.e., a polyester-based resin composition containing a polyester-based resin as a main component. In one or more embodiments of the present invention, when the total weight of the polyester-based resin composition is taken as 100% by weight, the “polyester-based resin composition containing a polyester-based resin as a main component” contains the polyester-based resin in an amount of 67% by weight or more, preferably 75% by weight or more, even more preferably 85% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more.

From the viewpoint of physical properties, versatility, and the cost, the polyester-based resin may be one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate. In the present disclosure, the “copolymerized polyester mainly containing polyalkylene terephthalate” refers to a copolymerized polyester containing polyalkylene terephthalate in an amount of 80 mol % or more.

Polyalkylene terephthalate is not particularly limited, and may be, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, or polycyclohexane dimethylene terephthalate.

The copolymerized polyester mainly containing polyalkylene terephthalate is not particularly limited, and may be, for example, a copolymerized polyester mainly containing polyalkylene terephthalate such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, or polycyclohexane dimethylene terephthalate, and further containing other copolymerizable components.

Examples of the other copolymerizable components include: polycarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, trimellitic acid, pyromellitic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid, and their derivatives; dicarboxylic acids and their derivatives containing sulfonates such as 5-sodiumsulfoisophthalic acid and dihydroxyethyl 5-sodiumsulfoisophthalate; 1,2-propanediol; 1,3-propanediol; 1,4-butanediol; 1,6-hexanediol; neopentyl glycol; 1,4-cyclohexanedimethanol; diethylene glycol; polyethylene glycol; trimethylolpropane; pentaerythritol; 4-hydroxybenzoic acid; ε-caprolactone; and an ethylene glycol ether of bisphenol A.

The copolymerized polyester may be produced by adding a small amount of other copolymerizable components to polyalkylene terephthalate serving as a main component, and allowing them to react with each other, from the viewpoint of stability and ease of operation. Examples of the polyalkylene terephthalate include a polymer of terephthalic acid and/or its derivatives (e.g., methyl terephthalate) and alkylene glycol. The copolymerized polyester may be produced by adding a small amount of monomer or oligomer component serving as other copolymerizable components, to a mixture of terephthalic acid and/or its derivatives (e.g., methyl terephthalate) and alkylene glycol, used for polymerization of polyalkylene terephthalate serving as a main component, and subjecting them to polymerization.

It is sufficient that the copolymerized polyester has a structure in which the other copolymerizable components are polycondensed on the main chain and/or side chain of polyalkylene terephthalate serving as a main component, and the copolymerization method and the like are not particularly limited.

Specific examples of the copolymerized polyester mainly containing polyalkylene terephthalate include a polyester obtained through copolymerization of polyethylene terephthalate serving as a main component with one compound selected from the group consisting of an ethylene glycol ether of bisphenol A, 1,4-cyclohexanedimethanol, isophthalic acid, and dihydroxyethyl 5-sodiumsulfoisophthalate.

Polyalkylene terephthalate and the copolymerized polyester mainly containing polyalkylene terephthalate may be used alone or in a combination of two or more. In particular, polyethylene terephthalate; polypropylene terephthalate; polybutylene terephthalate; a polyester obtained through copolymerization of polyethylene terephthalate serving as a main component with an ethylene glycol ether of bisphenol A; a polyester obtained through copolymerization of polyethylene terephthalate serving as a main component with 1,4-cyclohexanedimethanol; a polyester obtained through copolymerization of polyethylene terephthalate serving as a main component with isophthalic acid; a polyester obtained through copolymerization of polyethylene terephthalate serving as a main component with dihydroxyethyl 5-sodiumsulfoisophthalate, and the like may be used alone or in a combination of two or more.

The intrinsic viscosity (alternatively referred to as “IV value”) of the polyester-based resin is not particularly limited, but may be 0.3 or more and 1.2 or less, or 0.4 or more and 1.0 or less. If the intrinsic viscosity is 0.3 or more, the mechanical strength of the obtained fiber does not decrease, and there is no risk of dripping during a combustion test. On the other hand, if the intrinsic viscosity is 1.2 or less, the molecular weight is not too large, and the melt viscosity is not too high, and thus it is easy to perform melt spinning, and the fineness is likely to be uniform.

The polyester-based resin composition constituting the core part may further contain other resins in addition to the polyester-based resin serving as a main component resin. Examples of the other resins include a polyamide-based resin, a vinyl chloride-based resin, a modacrylic-based resin, a polycarbonate-based resin, a polyolefin-based resin, and a polyphenylenesulfide-based resin. These resins may be used alone or in a combination of two or more.

From the viewpoint of obtaining a touch and appearance closer to those of human hair and further improving the curling properties and curl retention properties, it is preferable that the core part of the core-sheath conjugate fiber for artificial hair is comprised of a polyester-based resin composition containing, as a main component, one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate, and it is more preferable that the sheath part of the core-sheath conjugate fiber for artificial hair is comprised of a polyamide-based resin composition containing, as a main component, a polyamide-based resin mainly containing at least one selected from the group consisting of Nylon 6 and Nylon 66.

In one or more embodiments of the present invention, a flame retardant may be used from the viewpoint of flame retardance. Examples of the flame retardant include a bromine-containing flame retardant and a phosphorus-containing flame retardant. Examples of the phosphorus-containing flame retardant include a phosphoric acid ester amide compound and an organic cyclic phosphorus-based compound. Examples of bromine-based flame retardants include, but are not particularly limited to, for example: a brominated epoxy-based flame retardant; bromine-containing phosphoric acid esters such as pentabromotoluene, hexabromobenzene, decabromodiphenyl, decabromodiphenyl ether, bis(tribromophenoxy)ethane, tetrabromophthalic anhydride, ethylene bis(tetrabromophthalimide), ethylene bis(pentabromophenyl), octabromotrimethylphenylindan, and tris(tribromoneopentyl)phosphate; brominated polystyrenes; brominated polybenzyl acrylates; a brominated phenoxy resin; brominated polycarbonate oligomers; tetrabromobisphenol A and tetrabromobisphenol A derivatives such as tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(allylether), and tetrabromobisphenol A-bis(hydroxyethyl ether); bromine-containing triazine compounds such as tris(tribromophenoxy)triazine; and bromine-containing isocyanuric acid compounds such as tris(2,3-dibromopropyl)isocyanurate. Of these compounds, it is preferable to use a brominated epoxy-based flame retardant from the viewpoint of heat resistance and flame retardance.

A brominated epoxy-based flame retardant having an epoxy group or tribromophenol at a molecular end thereof may be used as a raw material. The structure of the brominated epoxy-based flame retardant after melt kneading is not particularly limited, but it is preferable that 80 mol % or more of the structure is comprised of a constituent unit represented by the formula (1) below when the total number of constituent units each represented by the formula (1) below and constituent units obtained by at least partially modifying the formula (1) below is taken as 100 mol %. The structure of the brominated epoxy-based flame retardant may change at a molecular end thereof after melt kneading. For example, a molecular end of the brominated epoxy-based flame retardant may be substituted by a hydroxyl group, a phosphate group, a phosphonic acid group, or the like other than an epoxy group or tribromophenol, or may be bound to a polyester component through an ester group.

Furthermore, part of the structure of the brominated epoxy-based flame retardant, other than the molecular end, may be changed. For example, the brominated epoxy-based flame retardant may have a branched structure in which the secondary hydroxyl group and the epoxy group are bound. Also, part of the bromine of the formula (1) above may be eliminated or added, as long as the bromine content in the molecules of the brominated epoxy-based flame retardant does not change significantly.

For example, a polymeric brominated epoxy-based flame retardant as represented by the formula (2) below may be used as the brominated epoxy-based flame retardant. In the formula (2) below, m is 1 to 1000. Examples of the polymeric brominated epoxy-based flame retardant represented by the formula (2) below include a commercially available product such as a brominated epoxy-based flame retardant (product name “SR-T2M′P”) manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.

For example, it is preferable that the core part and/or the sheath part contains a brominated epoxy flame retardant in an amount of 5 parts by weight or more and 40 parts by weight or less with respect to 100 parts by weight of the main component resin, although there is no limitation thereto. For example, from the view point of heat resistance and flame retardance, it is preferable that the core part is comprised of a polyester-based resin composition that contains 100 parts by weight of one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate and 5 parts by weight or more and 40 parts by weight or less of a brominated epoxy flame retardant, and the sheath part is comprised of a polyamide-based resin composition that contains 100 parts by weight of a polyamide-based resin mainly containing at least one selected from the group consisting of Nylon 6 and Nylon 66 and 5 parts by weight or more and 40 parts by weight or less of a brominated epoxy flame retardant.

In one or more embodiments of the present invention, a flame retardant auxiliary may be used in combination. The flame retardant auxiliary is not particularly limited, but it is preferable to use an antimony-based compound and a composite metal including antimony from the viewpoint of flame retardance. Examples of the antimony-based compound include antimony trioxide, antimony tetraoxide, antimony pentoxide, sodium antimonate, potassium antimonate, and calcium antimonate. It is more preferable to use one or more selected from the group consisting of antimony trioxide, antimony pentoxide, and sodium antimonate, from the viewpoint of improving the flame retardance and the influence on a touch.

For example, it is preferable that the core part and/or the sheath part contains the flame retardant auxiliary in an amount of 0.1 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the main component resin, although there is no limitation thereto.

In particular, when the polyamide-based resin composition constituting the sheath part contains the flame retardant auxiliary, appropriate asperities are formed on the surface of the fiber, and a core-sheath conjugate fiber for artificial hair having an appearance with a low gloss dose to that of human hair as well as flame retardance is obtained.

As necessary, the core-sheath conjugate fiber for artificial hair may contain various types of additives such as a heat-resistant agent, a stabilizer, a fluorescer, an antioxidant, and an antistatic agent, within a range that does not inhibit the effects of one or more embodiments of the present invention.

Method for Producing Core-Sheath Conjugate Fiber

In one or more embodiments of the present invention, it is possible to produce the core-sheath conjugate fiber for artificial hair by melt-kneading resin compositions that respectively constitute the core part and the sheath part individually using various types of ordinary kneaders, and then performing melt spinning using a core-sheath conjugate nozzle.

For example, a core component is prepared by dry blending components such as the above-described polyester-based resin and the brominated epoxy-based flame retardant, and melt-kneading the obtained polyester-based resin composition using any of various ordinary kneaders. On the other hand, a sheath component is prepared by dry blending components such as the above-described polyamide-based resin and the brominated epoxy-based flame retardant, and melt-kneading the obtained polyamide-based resin composition using any of various ordinary kneaders. The core-sheath conjugate fiber can be produced by melt spinning the core component and the sheath component using a conjugate spinning nozzle.

Examples of the kneaders include a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, and a kneader. Of these kneaders, it is preferable to use a twin-screw extruder from the viewpoint of adjusting the kneading degree and easily performing the operation.

In a melt spinning method, for example, in the case of a polyester-based resin composition, melt spinning is performed while the temperatures of an extruder, a gear pump, a nozzle, and the like are set to 250° C. or more and 300° C. or less, and in the case of a polyamide-based resin composition, melt spinning is performed while the temperatures of an extruder, a gear pump, a nozzle, and the like are set to 260° C. or more and 320° C. or less, after which the extruded yarns are allowed to pass through a heated tube, cooled to a temperature not higher than the glass transition points of the resins, and wound up at a speed of 50 m/min or more and 5000 m/min or less, and thus extruded yarns (undrawn yarns) are obtained.

Specifically, during the melt spinning, the polyester-based resin composition that constitutes the core part is supplied from a core-part extruder of a melt spinning machine, the polyamide-based resin composition that constitutes the sheath part is supplied from a sheath-part extruder of the melt spinning machine, a molten polymer is discharged from a core-sheath conjugate spinning nozzle (pores) with a predetermined shape, and thus extruded yarns (undrawn yarns) are obtained.

It is preferable that the extruded yarns (undrawn yarns) are hot drawn. The drawing may be performed by either a two-step method or a direct drawing method. In the two-step method, the extruded yarns are wound once, and then drawn. In the direct drawing method, the extruded yarns are drawn continuously without winding. The hot drawing may be performed by a single-stage drawing method or a multi-stage drawing method that includes two or more stages. The heating means for the hot drawing may be a heating roller, a heat plate, a steam jet apparatus, or a hot water bath, which can be used in combination as desired.

In one or more embodiments of the present invention, it is also possible to make the touch and texture closer to those of human hair, by adding an oil solution such as a fiber treating agent and a softener to the core-sheath conjugate fiber for artificial hair.

Examples of the fiber treating agent include a silicone-based fiber treating agent and a non-silicone-based fiber treating agent for improving the touch and the combing property.

In one or more embodiments of the present invention, the core-sheath conjugate fiber for artificial hair may be subjected to gear crimping. In this case, it is possible to make the fiber gently curved and have a natural appearance, and to reduce the contact between fibers, thereby improving the combing property.

In the gear crimping, typically, a fiber heated to the softening temperature or more is caused to pass through a portion between two meshing gears, so that the shape of the gears is transferred to the fiber, and the fiber is thus curved. Furthermore, as necessary, it is also possible to make a fiber curled in different shapes by heat-treating the core-sheath conjugate fiber for artificial hair at different temperatures during the fiber production processes.

Hair Ornament Product

In one or more embodiments of the present invention, the core-sheath conjugate fiber for artificial hair can be suitably used for a hair ornament product. There is no particular limitation on the hair ornament product, but the hair ornament product may be at least one selected from the group consisting of a hair wig, a hairpiece, weaving hair, a hair extension, braided hair, a hair accessory, and doll hair, or a hair wig or weaving hair from the viewpoint of allowing the core-sheath conjugate fiber to more effectively exhibit the sufficiently high curl setting property according to one or more embodiments of the present invention.

The hair ornament product may be constituted only by the core-sheath conjugate fiber for artificial hair of one or more embodiments of the present invention, or comprised of the core-sheath conjugate fiber for artificial hair of one or more embodiments of the present invention combined with other core-sheath conjugate fibers for artificial hair and natural fibers such as human hair and animal hair.

EXAMPLES

Hereinafter, one or more embodiments of the present invention will be more specifically described by way of examples. Note that one or more embodiments of the present invention are not limited to these examples.

The measuring methods and the evaluation methods used in the examples and comparative examples are as follows.

Single Fiber Fineness

The measurement was performed using an autovibro type fineness measuring apparatus “Denier Computer type DC-11” (manufactured by Search), and an average of measured values of 30 samples was calculated and taken as the single fiber fineness.

Curl Setting Property

Filaments formed into a hair weft were wound around a pipe with a diameter of <p 32 mm at room temperature (23° C.), and curls were set for 60 minutes at 120° C. and aged for 60 minutes at room temperature (23° C.). Then, ends on one side of the curled filaments were fixed to suspend the filaments, and the length of the filaments after the curl setting was measured. The length was taken as an index of the curl setting property, and when the length was 17 cm or less, it was determined that curls could be set.

Exposure of Core Part

Fibers were bundled at room temperature (23° C.) and fixed with a shrinkage tube such that the fiber bundle (total fineness: 550 dtex) was not displaced, after which the fiber bundle was cut using a cutter, and whether or not the core part was exposed was evaluated through visual observation or evaluated by observing cross sections of the cut fibers using a laser microscope (“VK-9500” manufactured by Keyence Corporation).

Shape of Fiber Cross Section

Fibers were bundled at room temperature (23° C.) and fixed with a shrinkage tube such that the fiber bundle (total fineness: 550 dtex) was not displaced, after which the bundle was cut in round slices using a cutter, and thus a fiber bundle for cross section observation was prepared. An image of this fiber bundle was captured using a laser microscope (“VK-9500” manufactured by Keyence Corporation) at a magnification of 500 times, and thus a photograph of a fiber cross section was obtained. The core-to-sheath area ratio, L/S, and Lc/Sc were determined based on the photograph of the fiber cross section.

Touch

Sensory evaluation by professional hairstylists was performed in four stages below.

A: Very good touch similar to that of human hair B: Good touch although it is slightly poor compared with that of human hair C: Bad touch that is poor compared with that of human hair D: Bad touch that is significantly poor compared with that of human hair

Combing Property

Fibers whose curls were completely stretched were cut to have a length of 63.5 cm, and 5.0 g of thus obtained fibers with a fiber length of 63.5 cm was bundled. Subsequently, the fiber bundle was bound with a string at the middle thereof, folded in half, and fixed at the string portion, and thus a fiber bundle for hair iron treatment was prepared. Next, the fiber bundle was heated and crimped five times from the root at which the fiber bundle was fixed to the ends, using a hair iron (“Izunami ITC450 flat iron” manufactured by Izunami. Inc, U.S.) heated to 180° C., and thus a fiber bundle for combing property evaluation was prepared. Subsequently, a comb for combing hair (“Matador Professional 386.8 1/2F” made in Germany) was passed through the fiber bundle for combing property evaluation 100 times from the root at which the fiber bundle was fixed to the ends, and the combing property was evaluated according to the following criteria based on the number of fibers deformed or split.

A: Number of fibers deformed or split after a comb is passed through the fibers 100 times is less than 10, and the comb can be passed through the fibers to the ends without resistance. B: Number of fibers deformed or split after a comb is passed through the fibers 100 times is 10 or more and less than 30, and the comb can be passed through the fibers although the resistance somewhat significantly increases during the passing process. C: Number of fibers deformed or split after a comb is passed through the fibers 100 times is 30 or more and less than 100, and the comb cannot be passed through the fibers once or more and less than 20 times due to the resistance having increased during the passing process. D: Number of fibers deformed or split after a comb is passed through the fibers 100 times is 100 or more, and the comb cannot be passed through the fibers 20 times or more due to the resistance having increased during the passing process.

Example 1

20 parts by weight of a brominated epoxy-based flame retardant (product name “SR-T2MP” manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) and 2 parts by weight of sodium antimonate (product name “SA-A” manufactured by NIHON SEIKO CO., LTD.) were added to 100 parts by weight of polyethylene terephthalate pellets (EastPET product name “A-12” manufactured by East West Chemical Private Limited, hereinafter also referred to as “PET”), the mixture was dry blended, then supplied to a twin-screw extruder, melt-kneaded at a barrel setting temperature of 280° C., and pelletized, and thus a polyester-based resin composition was obtained.

Next, 20 parts by weight of a brominated epoxy-based flame retardant (product name “SR-T2MP” manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) and 2 parts by weight of sodium antimonate (product name “SA-A” manufactured by NIHON SEIKO CO., LTD.) were added to 100 parts by weight of Nylon 6 (product name “A1030BRL” manufactured by UNITIKA LTD., hereinafter also referred to as “PA6”), the mixture was dry blended, then supplied to a twin-screw extruder, melt-kneaded at a barrel setting temperature of 260° C., and pelletized, and thus a polyamide-based resin composition was obtained.

Next, the polyester-based resin composition and the polyamide-based resin composition in the form of pellets were supplied to extruders, extruded from a core-sheath conjugate spinning nozzle (pores) having a flatness ratio and a shape shown in Table 1 below, and wound up at a speed of 40 to 200 m/min, and thus undrawn yarns of core-sheath conjugate fibers each including a core part comprised of the polyester-based resin composition and a sheath part comprised of the polyamide-based resin composition, having a core-to-sheath area ratio of core:sheath=5:5, and a cross sectional shape shown in Table 1 below were obtained. The flatness ratio of the nozzle is the ratio between the length of a major axis and the length of a minor axis in a cross section of the nozzle, the major axis being a line segment with the largest length among an axisymmetric axis and line segments connecting any two points on the outer circumference of the cross section so as to be in parallel to the axisymmetric axis, and the minor axis being a line segment with the largest length among line segments connecting any two points on the outer circumference of the nozzle cross section so as to be perpendicular to the major axis.

The obtained undrawn yarns were drawn to 3 times while being wound up at a speed of 45 m/min using a heat roll at 85° C., and subsequently heat-treated by being wound up at a speed of 45 m/min using a heat roll heated to 200° C. After application of a polyether-based oil solution (product name “KWC-Q” manufactured by Marubishi Oil Chemical Corporation) in an amount of 0.20% omf (by oil pure weight percentage with respect to the dry fiber weight), the yarns were dried, and thus a core-sheath conjugate fiber having a single fiber fineness shown in Table 1 below was obtained.

Example 2

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the resin used for the sheath part was changed to Nylon 66 (product name “AMILAN CM3001” manufactured by Toray Industries, Inc.), the barrel setting temperature during pelletization was changed to 280° C., and the core-to-sheath area ratio was changed to core:sheath=7:3.

Example 3

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the core-to-sheath area ratio was changed to core:sheath=8:2.

Example 4

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the nozzle flatness ratio was changed to 1.4.

Comparative Example 1

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the shape of the nozzle was changed as shown in Table 1 below.

Comparative Example 2

A core-sheath conjugate fiber was obtained in a similar way to that of Example 2, except that the shape of the nozzle was changed as shown in Table 1 below.

Comparative Example 3

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the shape of the nozzle was changed as shown in Table 1 below.

Comparative Example 4

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the core-to-sheath area ratio was changed to core:sheath=2:8 and the shape of the nozzle was changed as shown in Table 1 below.

Comparative Example 5

A core-sheath conjugate fiber was obtained in a similar way to that of Example 1, except that the core-to-sheath area ratio was changed to core:sheath=9:1.

Comparative Example 6

A core-sheath conjugate fiber was obtained in a similar way to that of Example 4, except that the shape of the nozzle was changed as shown in Table 1 below.

The fibers of the examples and the comparative examples were observed and evaluated in terms of whether or not the core part was exposed and the cross sectional shapes of the fibers as described above. Also, the fibers of the examples and the comparative examples were evaluated in terms of the curl setting property, touch, and combing property as described above. Table 1 shows the results.

TABLE 1 Com. Com. Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Main component PET PET PET PET PET PET PET PET PET PET resin (core) Main component PA6 PA66 PA6 PA6 PA6 PA66 PA6 PA6 PA6 PA6 resin (sheath) Core-to-sheath 5:5 7:3 8:2 5:5 5:5 7:3 5:5 2:8 9:1 5:5 ratio (area ratio) Nozzle flatness 1.2 1.2 1.2 1.4 1.2 1.2 1 1.2 1.2 1.4 ratio Nozzle cross Flat two-lobed shape Flat two- Flat two- Circle Flat two- Flat two- Flat two- sectional shape lobed shape lobed shape lobed shape lobed shape lobed shape (fiber) Nozzle cross Modified flat Flat two- Flat two- Circle Ellipse Modified flat Flat two- sectional shape two-lobed shape lobed shape lobed shape two-lobed lobed shape (core part) (with pair of shape protrusions) (with pair of protrusions) Single fiber 58 62 63 58 58 62 58 54 65 58 fineness (dtex) Cross sectional Flat two-lobed shape Flat two- Flat two- Circle Flat two- Flat two- Flat two- shape of fiber lobed shape lobed shape lobed shape lobed shape lobed shape Cross sectional Modified flat Flat two- Flat two- Circle Ellipse Modified flat Flat two- shape of two-lobed shape lobed shape lobed shape two-lobed lobed shape core part (with pair of shape protrusions) (with pair of protrusions) Photograph of FIG. 2 — — — FIG. 3 — FIG. 4 — — — cross section L/S 1.14 1.20 1.21 1.39 1.22 1.25 1.00 1.20 1.19 1.46 Lc/Sc 1.07 1.05 1.07 1.20 1.60 1.54 1.22 1.65 1.07 2.10 Curl length (cm) 16 15 14 17 19 18 16 21 — 19 Exposure of No No No No No No No No Yes No core part Touch A B B A A B C C D A Combing B B B A B B D A C A property

FIG. 2 is a laser microscopic photograph of a fiber cross section of the fiber of Example 1. As can be seen from FIG. 2, the core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape, and the core part has a modified flat two-lobed cross sectional shape that includes a pair of protrusions protruding from the center side toward the outer circumferential side along a minor axis direction of the fiber cross section. FIG. 3 is a laser microscopic photograph of a fiber cross section of the fiber of Comparative Example 1. As shown in FIG. 3, the core-sheath conjugate fiber for artificial hair and the core part thereof both have flat two-lobed cross sectional shapes. FIG. 4 is a laser microscopic photograph of a fiber cross section of the fiber of Comparative Example 3. As shown in FIG. 4, the core-sheath conjugate fiber for artificial hair and the core part thereof both have substantially circular cross sectional shapes.

As can be seen from Table 1, in the cases of the fibers of Examples 1 to 4, the curl setting property was good, the core part was not exposed, the touch was close to that of human hair, and the combing property was also good.

On the other hand, the curl setting property was poor in the cases of the fibers of Comparative Examples 1, 2, and 6 in which the cross sectional shape of the core part did not include a pair of protrusions. As for the fiber of Comparative Example 3, which had a circular fiber cross section, the fiber surface did not have asperities, and therefore, the appearance of the fiber was unnatural, and a fiber having a good touch and a good combing property could not be obtained. In the case of the fiber of Comparative Example 4 in which the core-to-sheath area ratio was 2:8, the curl setting property was poor because the amount of the core part was too small. In the case of the fiber of Comparative Example 5 in which the core-to-sheath area ratio was 9:1, the sheath part became too thin, and accordingly, the core part was exposed and both the touch and the combing property were very poor.

One or more embodiments of the present invention may include the following embodiments, for example, although there is no particular limitation thereto.

[1] A core-sheath conjugate fiber for artificial hair including a core part and a sheath part,

wherein the core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape or an elliptical cross sectional shape, and has a core-to-sheath area ratio of core:sheath=3:7 to 8:2 in a fiber cross section,

the sheath part is comprised of a polyamide-based resin composition that contains a polyamide-based resin, and

the core part has a modified flat two-lobed cross sectional shape or a modified elliptical cross sectional shape including a pair of protrusions protruding from the center side toward the outer circumferential side along a minor axis direction of the fiber cross section.

[2] The core-sheath conjugate fiber for artificial hair according to [1], wherein the core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape and the core part has a modified flat two-lobed cross sectional shape.

[3] The core-sheath conjugate fiber for artificial hair according to [1] or [2], wherein the core part is comprised of a polyester-based resin composition that contains one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate.

[4] The core-sheath conjugate fiber for artificial hair according to any one of [1] to [3], wherein the sheath part is comprised of a polyamide-based resin composition that contains a polyamide-based resin mainly containing at least one selected from the group consisting of Nylon 6 and Nylon 66.

[5] A hair ornament product including the core-sheath conjugate fiber for artificial hair according to any one of [1] to [4].

[6] The hair ornament product according to [5], wherein the hair ornament product is one selected from the group consisting of a hair wig, a hairpiece, weaving hair, a hair extension, braided hair, a hair accessory, and doll hair.

[7] A method for producing the core-sheath conjugate fiber for artificial hair according to any one of [1] to [4], including a step of melt spinning a core part resin composition and a sheath part resin composition using a core-sheath conjugate nozzle.

LIST OF REFERENCE NUMERALS

-   -   1 Core-sheath conjugate fiber for artificial hair (cross         section)     -   10 Sheath part     -   20 Core part     -   30 Protrusion

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A core-sheath conjugate fiber for artificial hair comprising: a core part; and a sheath part, wherein: the core-sheath conjugate fiber for artificial hair has a flat two-lobed cross sectional shape and a core-to-sheath area ratio of core:sheath=3:7 to 8:2 in a fiber cross section, the sheath part is comprised of a polyamide-based resin composition that comprises a polyamide-based resin, and the core part has a modified elliptical cross sectional shape including a pair of protrusions protruding from a center side toward an outer circumferential side along a minor axis direction of the fiber cross section.
 2. The core-sheath conjugate fiber for artificial hair according to claim 1, wherein the core part is comprised of a polyester-based resin composition that comprises one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate.
 3. The core-sheath conjugate fiber for artificial hair according to claim 1, wherein the polyamide-based resin mainly contains at least one selected from the group consisting of Nylon 6 and Nylon
 66. 4. The core-sheath conjugate fiber for artificial hair according to claim 1, wherein the core-sheath conjugate fiber is a concentric core-sheath conjugate fiber.
 5. A method for producing the core-sheath conjugate fiber for artificial hair according to claim 1, comprising a step of melt spinning a core part resin composition and a sheath part resin composition with a core-sheath conjugate nozzle.
 6. A hair ornament product comprising the core-sheath conjugate fiber for artificial hair according to claim
 1. 7. The hair ornament product according to claim 6, wherein the hair ornament product is one selected from the group consisting of a hair wig, a hairpiece, weaving hair, a hair extension, braided hair, a hair accessory, and doll hair.
 8. The hair ornament product according to claim 6, wherein the core part is comprised of a polyester-based resin composition that comprises one or more of polyester-based resins selected from the group consisting of polyalkylene terephthalate and a copolymerized polyester mainly containing polyalkylene terephthalate.
 9. The hair ornament product according to claim 6, wherein the polyamide-based resin mainly contains at least one selected from the group consisting of Nylon 6 and Nylon
 66. 10. The hair ornament product according to claim 6, wherein the core-sheath conjugate fiber is a concentric core-sheath conjugate fiber. 